FI72548C - ANORDNING VID TORKPARTIET AV PAPPERSMASKIN. - Google Patents

Description

1 72548

Device related to the drying section of a paper machine

The invention relates to a device associated with a drying section of a paper machine, which drying section comprises a drying cylinder and a high-temperature hood or hoods arranged thereon, to which fresh steam produced in the boiler room is fed to the drying cylinder and blown air is supplied to the high-temperature hood or hoods.

The object of the present invention is to improve the energy utilization rate 10 by utilizing the energy content of the exhaust air of the drying plant.

It is known and now common that the exhaust air of high-temperature lacquers is released into the atmosphere after it has heated fresh air to 150-250 °. The condensate generated in the drying cylinder-15 is normally expanded in two stages to ambient pressure and led to the boiler room. The steam used to heat the cylinder is produced in the boiler room. It is disadvantageous that the reduction of the condensate pressure generates a large amount of expansion steam which must be condensed in the condenser by means of cooling water. The energy content of this steam is then wasted. The expanded condensate is pumped by means of a feed water pump from the ambient pressure to the pressure of the steam, i.e. the boiler, and is then evaporated in the boiler. This requires a large amount of energy. The energy content of the steam 25 is then used in a drying plant for drying. Exhaust air vapor still has a relatively high energy content, which is currently largely wasted as it is released into the atmosphere.

In addition, it has been proposed in AT patent publication 374 214, 30 that the residual heat of the drawing hoods of paper machines be utilized by means of a heat pump. In this case, a compressor-turbine engine is used, in which the compressor is connected to the exhaust air line and the high-pressure part is connected to the turbine via a heat exchanger and the separation power is brought from outside.

This device is not suitable for the context of the invention, since it is a draft with an exhaust air temperature of 80 °.

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Finally, DE-A-3 003 718 discloses a method and apparatus for drying paper or cellulose in which the drying takes place directly by superheated steam. The installed heat exchanger is here made as a steam superheater and the steam stream passing through the condenser 5 is then discharged as condensate.

The object of the invention is to utilize the energy content of the exhaust air in a drying section of a paper machine comprising a drying cylinder fed with fresh steam and a high temperature dome to which blowing air is introduced, thus reducing the need for primary energy for drying and providing a device that can be installed in existing plants. According to the invention, this object is achieved by connecting a steam separator to the exhaust cylinder in a manner known per se to separate the exhaust steam, the steam separator being connected to to a second heat exchanger to which a supply line is connected to conduct the heated fresh air to the high temperature dome. Thus, a heat exchanger is connected to the exhaust air stream for energy recovery, where the pressurized condensate is evaporated. The condensate generated in the drying cylinder is led at a corresponding pressure to the exhaust air heat exchanger, where it evaporates under the influence of the energy content of the exhaust air. Next, the steam is pumped by the compressor to the steam pressure of the cylinder. In another alternative, the condensate 30 is already brought to the cylinder pressure by means of a pump before the exhaust air heat exchanger. The invention is thus based on the idea that the heat content of the exhaust air is used for the production of steam; the heat exchanger is a steam generator heated by hot exhaust air; the steam flow through the compressor is raised to the required pressure level and, together with the 3 72548 fresh steam, is returned to the machine, thus saving larger amounts of fresh steam.

The invention will be described in more detail by means of an application example.

Figure 1 shows an apparatus for utilizing the energy of a drying section.

Figure 2 shows a variation of Figure 1.

Figure 3 shows a device without a mechanical booster.

As can be seen from Fig. 1, a high temperature dome 1 mounted around the drying cylinder 2 is used in the drying section of the paper machine. The paper web to be dried is passed around the drying cylinder 2 and is heated by steam in the drying cylinder 2, whereby the moisture contained in the material-15 web is transferred to the heated blowing air introduced into the high temperature dome 1 and removed thereby. The device according to the invention is connected in order to utilize the otherwise exhaust air. Along the fresh steam line 3, the fresh steam produced in the boiler room enters the pressure-reducing valve 4 and is led along the supply line 5 to the drying cylinder 2 to heat it. From the drying cylinder 2 the condensate line 6 leads to the first steam separator 19. From here the residual steam used for re-drying is led along the circulating steam line 20 to the compressor 21 driven by the motor 22. The condenser of the steam separator 19 then passes through the branch 30 26 to the condenser 29 and is cooled with cooling water 33 and used as condensate. Further, the water or condensate coming from the steam separator 25 is transferred along the boiler feed water line 27 and via the pump 28 to the boiler room. The branch body 30 becomes condensate along the condensate pipe 24 to a heat exchanger 14, which is heated by air removed from the high temperature hood 1 via the exhaust air line 10. Finally, the steam-35 knurled condensate is introduced from the heat exchanger 14 to the T-piece 32 and then to the supply line 5 along the pressure line 23.

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The exhaust air of the high temperature dome 1 is fed after the energy has been transferred in the exhaust air heat exchanger 14 to the second fresh air heat exchanger 15 via the exhaust air line 10 and is then transferred to the outside air by the exhaust air fan 5. The air sucked through the fan 17 and the fresh air line 16 is heated in the heat exchanger 15 and transferred through the air line 13 and the fan 12 to the combustion chamber 8 and heated to the temperature of the blowing air. The auxiliary air line 9 leads to the combustion chamber 8. Thus, the heated air 10 enters the high-temperature dome 1 as blowing air along the blowing air line 7. A recirculating air line 11 is connected between the exhaust air line 10 and the air line 13 to raise the temperature of the blowing air.

Figure 2 shows a variant of the device with the same reference numerals. The difference is that the compressor 21 is placed in the circulating steam line 20 before the T-piece 32. Although the condenser line 24 requires a pump 34, the condensate pressure is raised to the cylinder pressure even before evaporation in the exhaust air heat exchanger 14 and the energy requirement of the compressor 20 is reduced.

Finally, a variant with no mechanical pressure increase is shown in Fig. 3, in which case the differences from Fig. 1 are mentioned here again. The steam separator 19 enters residual steam along the circulating steam line 20 directly to the steam jet-25 compressor, i.e. to the thermal compressor 35 and to the supply line 5.

This device creates a smaller amount of expansion vapor that needs to be condensed. The amount of cooling water is therefore significantly reduced. The amount of energy required to reach the cylinder pressure is greatly reduced due to evaporation when pressurized. Due to the steam generation in the system, the conduction losses of condensate and fresh steam are further reduced due to the smaller amount.

However, the biggest benefit is that the energy required for drying, which until now had to be produced with primary energy, is significantly reduced. It should also not be forgotten that the environment is less polluted when the exhaust air is better utilized.

Claims (5)

5,72548 An apparatus associated with a drying section of a paper machine, the drying section comprising a drying cylinder (2) and a high temperature hood (1) or more hoods arranged thereon, to which fresh steam produced in a boiler room is fed to the drying cylinder (2) and a high temperature hood (1) or hoods that a steam separator (19) is connected to the drying cylinder (2) in a sense to separate the exhaust steam, that the steam separator (19) is connected on the one hand by a circulating steam line (20) and a compressor (21) to a supply line (5) to the drying cylinder (2) on the other hand, the condensate line (24) of the steam separator (19) is connected via a heat exchanger (14) to the circulating steam line (20) and an exhaust air line (10) is led from the high temperature hood (1) to the heat exchanger (14) and the second heat exchanger (15). (15) is connected to a supply line for conducting heated fresh air to the high temperature-20 dome (1). Device according to Claim 1, characterized in that the compressor (21) is arranged in the circulating steam line (20) before or after the evaporated condensate supply point (32). Device according to Claim 1 or 2, characterized in that when the compressor (21) is arranged before the vaporized condensate supply point (32) in the circulating steam line (20), a pump (34) is connected to the condensate line (24). Device according to one of Claims 1 to 3, characterized in that the circulating steam line (20) is fed to a steam jet compressor (35). Device according to one of Claims 1 to 4, characterized in that a circulating air line (11) is arranged between the air outlet line (10) of the high-temperature hood (1) and the air line (13) coming from the heat exchanger (15).